A known industrial process for the conversion of hydrogen sulphide is the so-called Claus process. In a Claus process hydrogen sulphide is reacted with sulphur dioxide to elemental sulphur and water according to the Claus reaction.2 H2S+SO22 H2O+3/n Sn   (1)
Conventionally, this reaction is performed in several stages at temperatures in the range of from 200 to 240° C. and at near atmospheric pressures.
In conventional Claus processes, hydrogen sulphide is first separated from a hydrocarbon gas stream, e.g. by a solvent extraction process. After solvent regeneration, a hydrogen sulphide-rich gas is obtained, which is dealt with in the Claus process. About one third of the hydrogen sulphide in this gas is oxidized with air to sulphur dioxide in a burner, according to:2 H2S+3 O22 H2O+2 SO2   (2)
The sulphur dioxide subsequently reacts with the remaining hydrogen sulphide to elemental sulphur according to reaction (1).
The hydrogen sulphide has first to be separated from the remainder of the gas to prevent combustion of the hydrocarbons (or hydrogen) in the feed gas. It would be advantageous if hydrogen sulphide could be selectively oxidized, i.e. without the need to separate it from the remainder of the gas.
In P.D. Clark, Controlling CO2 emissions in large scale sour gas developments, Alberta Sulphur Research Limited, Quarterly Bulletin of ASRL, June 2008, page 45 to 55, a high pressure Claus process is disclosed wherein a sour natural gas stream is processed to remove hydrogen sulphide, without the need to separate the hydrogen sulphide from the natural gas. In this process one third of sour gas is combusted with pure oxygen to provide a gas comprising sulphur dioxide, carbon dioxide and water, the remaining two thirds of the sour gas are passed through a carbon bed to remove mercaptans and any other contaminants. Subsequently, the sulphur dioxide and water-comprising gas and the mercaptan-depleted sour gas are provided to a reactor and allowed to react over an alumina catalyst.
In WO2004007358, a method is provided for removing hydrogen sulphide from synthesis gas, without the need for a prior separation of the sulphur compounds from the synthesis gas. An oxidant used in the method of WO2004007358 is sulphur dioxide. Suitable catalyst mentioned in WO2004007358, include alumina (Al2O3) and titania (TiO2), which are two of the most used Claus catalyst. The examples of WO2004007358 only show the use of alumina catalyst.
The use of TiO2 catalysts has a number of advantages over the use of alumina catalyst, one being that TiO2 catalyses the hydrolysis of COS present in the feed stream. In conventional high temperature, low pressure Claus reactions, TiO2 catalysts show little to no deactivation. Methods as disclosed in Clark et al. and WO2004007358 are operated at much lower temperatures and elevated pressures than conventional high temperature, low pressure Claus reactions. It has been found that under such conditions the catalyst does show deactivation and consequently a lower hydrogen sulphide conversion after prolonged operation times.
There is a need in the art for a process for the direct selective oxidation of hydrogen sulphide comprised in gaseous hydrocarbon or hydrogen-comprising streams using a Claus catalyst for prolonged times without observing significant loss of hydrogen sulphide conversion.